Abstract: An engine includes a cylinder body, a cylinder head, and an ignition device including spark plugs. The engine also includes an intake device connected to intake ports, an exhaust device connected to exhaust ports, pistons, and a crankshaft connected to the pistons by connecting rods. Explosion intervals of the cylinders are 270°, 180°, 90°, and 180° as crank angles. The engine further includes a discomfort eliminator which, when the engine speed is lower than a predetermined value, makes the indicated mean effective pressure of at least one of two cylinders having an explosion interval of 90° lower than the indicated mean effective pressures of the other cylinders having an explosion interval of not 90°. The engine causes unequal-interval explosions but produces little change in the driving energy per unit time during an operating state in which an occupant is liable to feel torque fluctuations.

Abstract: A six-stroke engine includes a cylinder, a piston, a cylinder head, a combustion chamber, an intake port, an exhaust port, an intake valve, an exhaust valve, a fuel injector, and an ignition plug. The six-stroke engine includes a valve gear that operates the intake valve and the exhaust valve to execute an intake stroke, a compression stroke with ignition, an expansion stroke with combustion, an exhaust stroke, an expansion stroke without combustion, and a compression stroke without ignition. The valve gear opens, only for a predetermined period of time while the piston is located at top dead center, at least one of the intake valve and the exhaust valve within a period from the exhaust stroke to the intake stroke. A valve overlap state is produced at least once within the period from the exhaust stroke to the intake stroke.

Abstract: An engine includes a cylinder body, a cylinder head, and an ignition device including spark plugs. The engine also includes an intake device connected to intake ports, an exhaust device connected to exhaust ports, pistons, and a crankshaft connected to the pistons by connecting rods. Explosion intervals of the cylinders are 270°, 180°, 90°, and 180° as crank angles. The engine further includes a discomfort eliminator which, when the engine speed is lower than a predetermined value, makes the indicated mean effective pressure of at least one of two cylinders having an explosion interval of 90° lower than the indicated mean effective pressures of the other cylinders having an explosion interval of not 90°. The engine causes unequal-interval explosions but produces little change in the driving energy per unit time during an operating state in which an occupant is liable to feel torque fluctuations.

Abstract: A six-stroke engine includes a cylinder, a piston, a cylinder head, a combustion chamber, an intake port, an exhaust port, an intake valve, an exhaust valve, a fuel injector, and an ignition plug. The six-stroke engine includes a valve gear that operates the intake valve and the exhaust valve to execute an intake stroke, a compression stroke with ignition, an expansion stroke with combustion, an exhaust stroke, an expansion stroke without combustion, and a compression stroke without ignition. The valve gear opens, only for a predetermined period of time while the piston is located at top dead center, at least one of the intake valve and the exhaust valve within a period from the exhaust stroke to the intake stroke. A valve overlap state is produced at least once within the period from the exhaust stroke to the intake stroke.

Abstract: A six-stroke cycle engine includes an intake passage including a downstream end connected to a combustion chamber and no throttle valve therein, and an exhaust passage including a catalyst and an upstream end connected to the combustion chamber. The six-stroke cycle engine includes a first valve configured to open and close the intake passage, a second valve configured to open and close the exhaust passage, a valve gear configured to operate the first valve and the second valve so that an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke are executed, in this order, and to operate only the first valve so that a scavenging intake stroke and a scavenging exhaust stroke are executed, in this order, following the exhaust stroke. The valve gear includes a variable valve mechanism configured to continuously change an opening and closing timing and a lift amount of the first valve.

Abstract: A six-stroke cycle engine includes an intake passage including a throttle valve, and an exhaust passage including a catalyst. The six-stroke cycle engine includes a scavenging passage including a first end defined by a scavenging port and a second other end connected to the intake passage upstream of the throttle valve. The six-stroke cycle engine includes an intake valve, an exhaust valve, a scavenging valve, and a valve gear configured to operate these valves. The valve gear closes the scavenging valve and operates the intake valve and the exhaust valve so as to execute an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke, in this order. The valve gear also operates only the scavenging valve so as to execute a scavenging intake stroke and a scavenging exhaust stroke, in this order, following the exhaust stroke.

Abstract: A six-stroke engine includes a cylinder, a piston, a cylinder head, a combustion chamber, cylinder injector, a spark plug, an intake port, an exhaust port, an intake valve, an exhaust valve, a valve gear, and a control device. The valve gear operates the intake valve and the exhaust valve to execute six strokes including an intake stroke, a compression stroke without ignition, an expansion stroke without combustion, a compression stroke with ignition, an expansion stroke with combustion, and an exhaust stroke in this order. The control device is programmed to cause the cylinder injector to inject fuel and to energize the spark plug in the compression stroke with ignition.

Abstract: A six-stroke cycle engine includes an intake passage including a downstream end connected to a combustion chamber and no throttle valve therein, and an exhaust passage including a catalyst and an upstream end connected to the combustion chamber. The six-stroke cycle engine includes a first valve configured to open and close the intake passage, a second valve configured to open and close the exhaust passage, a valve gear configured to operate the first valve and the second valve so that an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke are executed, in this order, and to operate only the first valve so that a scavenging intake stroke and a scavenging exhaust stroke are executed, in this order, following the exhaust stroke. The valve gear includes a variable valve mechanism configured to continuously change an opening and closing timing and a lift amount of the first valve.

Abstract: A six-stroke cycle engine includes an intake passage including a throttle valve, and an exhaust passage including a catalyst. The six-stroke cycle engine includes a scavenging passage including a first end defined by a scavenging port and a second other end connected to the intake passage upstream of the throttle valve. The six-stroke cycle engine includes an intake valve, an exhaust valve, a scavenging valve, and a valve gear configured to operate these valves. The valve gear closes the scavenging valve and operates the intake valve and the exhaust valve so as to execute an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke, in this order. The valve gear also operates only the scavenging valve so as to execute a scavenging intake stroke and a scavenging exhaust stroke, in this order, following the exhaust stroke.

Abstract: A six-stroke engine includes a cylinder, a piston, a cylinder head, a combustion chamber, cylinder injector, a spark plug, an intake port, an exhaust port, an intake valve, an exhaust valve, a valve gear, and a control device. The valve gear operates the intake valve and the exhaust valve to execute six strokes including an intake stroke, a compression stroke without ignition, an expansion stroke without combustion, a compression stroke with ignition, an expansion stroke with combustion, and an exhaust stroke in this order. The control device is programmed to cause the cylinder injector to inject fuel and to energize the spark plug in the compression stroke with ignition.